An image sensor may be fabricated to have a large number (e.g. more than 1 million) of sensor elements (pixels) arranged in a defined pattern (e.g. a square grid). The pixels may be photodiodes, charge-coupled devices (CCD) or other photosensitive elements, that are adapted to convert electromagnetic radiation (e.g. visible light, infrared light) into electrical signals.
Recent advances in semiconductor technologies have enabled the fabrication of nanostructures, such as nanotubes, nanocavities, and nanowires. Among them, nanowires have drawn a lot of interest because of their usefulness as sensor elements in an image sensor. For instance, U.S. Patent Application Publication No. 2004/0075464 discloses a plurality of devices based on nanowires, herein incorporated by reference in its entirety. Discrete electronic devices such as transistors, photodiodes and photoconductors have been made successfully from nanostructures. It has been a challenge, however, to integrate and position such discrete electronic devices based on nanostructures in a functional apparatus, especially in a way that each of such devices can be individually controlled and addressed.
U.S. patent application Ser. Nos. 12/633,313 filed Dec. 8, 2009, and 12/575,221 filed Oct. 7, 2009, describe two methods for achieving this goal, which are herein incorporated by reference in their entirety. The first method includes forming a Cartesian (x-y) matrix wiring (e.g. aluminum) first and to then forming a nanowire array thereon. This method begins with a fabrication of a substrate which provides an x-y matrix wiring and components employing a conventional complementary metal-oxide-semiconductor (CMOS) fabrication process. Nanowires are then grown using a Vapor-Liquid-Solid (VLS) method in designated locations. However, the VLS growth generally requires temperatures that tend to damage the wiring and components on the substrate and tend to undesirably disturb pre-existing doping profile in the substrate.
The second method includes forming a nanowire array first by either a VLS growth or an etching method. Then, an x-y matrix of wiring is fabricated to electrically connect each nanowire in the nanowire array to external circuitry. This method requires nanoscale lithography on a non-planar surface.
Described hereinbelow are devices and methods of manufacturing the same, which include controlled integration of individually addressable nanostructures such as nanowires and nanopillars into a functional apparatus such as an image sensor, without the abovementioned problems.